Vol. 70.] FOSSIL FLORA OF THE KKNT COALFIELD. 79 



With regard to the paheobotanical horizons represented in Kent, 

 there is no indication at present of the presence of Upper Coal 

 Measures. It is true that there is still some doubt as to the 

 location o£ the highest measures in the held. But if Upper Coal 

 Measures occur at all, which, in my opinion, is more than unlikely, 

 they must lie out to sea in the unexplored ground beneath the 

 English Channel. So far as that portion of the coalfield which 

 underlies land is concerned, one can say without hesitation that the 

 highest beds represented belong to the Transition Coal Measures, 

 and in none of these has a typical Upper Coal Measure flora been 

 found to occur. 



The presence of Transition Coal Measures in Kent was first made 

 known by Prof. Zeiller 1 in 1892. In 1909 2 I showed that these 

 beds are well developed in the central region of the coalfield, and 

 in the present paper their distribution has been further traced. 



The present communication contains the first proof of the occur- 

 rence of Middle Coal Measures in this coalfield, and it has been 

 shown that these beds are there widely developed. 



This horizon, the Middle Coal Measures, is the lowest present in 

 the coalfield, so far as it is proved. I can find no evidence of 

 Lower Coal Measures, much less of Millstone Grits (which paheo- 

 botanically are simply the lowest beds of the Lower Coal Measures;, 

 and I very much doubt whether this horizon is represented in any 

 of the Armorican coalfields of England or Wales. A careful exami- 

 nation of the floras of the borings, recorded in the preceding pages, 

 which have passed through the lowest beds of the measures into the 

 Carboniferous Limestone Series, has not resulted in the recognition 

 of a typically Lower Coal Measure assemblage of plants at this 

 level. There is no change in the flora of these beds as compared 

 with that of the higher beds in the same boring: that is, the plants 

 indicate a Middle Coal Measure flora throuo-hout. 



I conclude, therefore, that only two horizons are represented in 

 the Kent coalfield — the Transition and the Middle Coal Measures — , 

 at least so far as the area yet proved is concerned. 



The examination of the floras of these new borings has resulted 

 in the most detailed study of the vegetation of the higher part of 

 the Middle and the lower part of the Transition Coal Measures 

 that has as yet been made in any British coalfield. It has con- 

 firmed the conclusion, arrived at from a knowledge of the fossil 

 floras of other coalfields, that there is no ' break ' between these 

 floras, but rather a perfectly gradual transition from the Middle to 

 the Transition type. For this reason, when near the borderland of 

 these two horizons, it is not possible sometimes to fix, by means 

 of the plants alone, the exact boundary between them withio several 

 hundred feet. But, bv correlating the lithological records of two or 

 more borings in connexion with their floras, it is usually possible to 

 arrive at an approximate, if somewhat arbitrary, line of demarcation, 



1 Zeiller (1892) & (1894). a Arber (1909). 



